This invention relates to a switch device for starting and stopping the rotation of a DC electric motor for opening and closing a window of a motor vehicle such as an automobile or for a similar purpose and more particularly to such a switch device for a DC electric motor operating at a high source voltage (such as 42V).
Automobiles currently make use of a 14V electrical system with source voltage of 12V. Since an increased number of electronic devices are being carried on automobiles, however, a 14V system is sometimes hardly capable of supplying sufficient power. As a result of global discussions in consortia representing both universities and industries in view of this problem, a consensus has been obtained from the point of view of safety to human bodies to adopt a voltage system that is three times higher, or a 42V system with source voltage of 36V. Examples of electrical equipment to be operated in a 42V electrical system include DC motors contained in a door for opening and closing a window (or so-called DC motors for operating a power window).
FIGS. 10A and 10B are respectively a structural diagram and a circuit diagram of a prior art switch device 1 for rotating (both in positive and negative directions) and stopping such a DC motor 2 for operating a power window. Such a switch device may typically be installed inside the elbow rest attached to the front or back seat of the vehicle or inside a door. FIGS. 10A and 10B show the switch device 1 when the DC motor 2 is stopped, that is, when a knob 3 therefor is not being operated. In what follows, this condition is referred to as the neutral condition.
The knob 3 is attached to a case 4 on a door such that it can be tilted by a specified angle both in clockwise and counter-clockwise directions, as shown in FIG. 10A. If the knob 3 is rotated in the clockwise direction, the window is closed (to be in the UP condition). If the knob 3 is rotated in the counter-clockwise direction, the window is opened (to be in the DOWN condition). If the force applied on the knob 3 is released, or if the finger is lifted therefrom, the knob 3 returns to its neutral position by the operations of a spring 5 and a plunger 6 buried inside the knob 3 and thereafter remains in this neutral condition.
The knob 3 has a downward protrusion 7 which is at a position as shown in FIG. 10A when the knob 3 is in the neutral position but swings to the left when the knob 3 is in the UP condition as shown in FIG. 12A and to the right when the knob 3 is in the DOWN condition (not shown in drawing).
Provided inside the case 4 is a switch unit 9 mounted to a printed circuit board 8 so as to function as a two-circuit two-contact switch of a momentary type. FIG. 11 shows an external view of this switch unit 9, comprising a housing 10, two common terminals 11 and 12 coming out of one side surface of the housing 10, one normally open terminal 13 coming out of the other side surface of the housing 10 and two normally closed terminals 14 and 15 coming out of the bottom surface of the housing 10. These terminals 11–15 are soldered to specified conductor circuits on the printed circuit board 8 so as to be connected to a power source line (or the +B line) 17, a grounding line 18 and the DC motor 2, as shown in FIG. 10B.
As shown in FIG. 10B, the switch unit 9 includes two switch mechanisms A and B adapted to operate mutually exclusively according to the position of a slider 28 on the upper surface of the switch unit 9. In the above, to be switched mutually exclusively means opening only the normally closed (NC) contact of either one of the switch mechanisms A and B, or closing only the normally open (NO) contact of that switch mechanism.
Explained more in detail, when the slider 28 is in the neutral condition, as shown in FIG. 10A, it is in the closed condition between the moving contact 19 and the NC contact 23 of the first switch mechanism A and between the moving contact 20 and the NC contact 24 of the second switch mechanism B. In this position, the NO contacts 21 and 22 of both switch mechanisms A and B are in open condition and the NC contacts 23 and 24 of both switch mechanisms A and B are in closed condition, as their names (NO and NC) indicate. If the slider 28 is moved to the left as indicated by arrow L in FIG. 11 to be in the UP condition, the closed condition between the moving contact 20 and the NC contact 24 of the second switch mechanism B is maintained but the NC contact 23 of the first switch mechanism A is released from the closed condition and a new closed condition is established between the moving contact 19 and the NO contact 21. Likewise, if the slider 28 is moved to the right as indicated by arrow R in FIG. 11 to be in the DOWN condition, the closed condition between the moving contact 19 and the NC contact 23 of the first switch mechanism A is maintained but the NC contact 24 of the second switch mechanism B is released from the closed condition and a new closed condition is established between the moving contact 20 and the NO contact 22.
The switching operations as described above are made possible by the movement of the slider 28 as well as by the designed shape of the bottom surface of the slider 28. FIGS. 11C and 11D are sectional views of the slider 28 taken respectively along lines 11C—11C and 11D and 11D of FIG. 11B. FIG. 11C shows that the right-hand half of the slider 28 is made thicker and FIG. 11D shows that the left-hand half of the slider 28 is made thicker. As will be explained below, the switching mechanisms A and B are switched in a mutually exclusive manner according to the positional relationship between these thickly made portions of the slider 28. It is to be noted that only one of the common terminals 11 and 12 and one of the normally closed terminals 14 and 15 are visible in FIG. 10A because the others of the common terminals and the normally closed terminals are hidden behind the front ones.
As explained above, the switch unit 9 described above functions as a two-circuit two-contact switch of a momentary type. This comes about because the moving contacts 19 and 20, the NO contacts 21 and 22 and the NC contacts 23 and 24 are connected respectively to the common terminals 11 and 12, the normally open terminal 13 and the normally closed terminals 14 and 15 such that the switching of contacts in two circuits (that is, the switching between the NO contact 21 and the NC contact 23 by the moving contact 19 and the switching between the NO contact 22 and the NC contact 24 by the moving contact 20) can be effected in a mutually exclusive manner.
The moving contacts 19 and 20 are attached at the tips of a mobile pieces 25 and 26 each in the form of a metallic spring plate, and these mobile pieces 25 and 26 are biased downwardly with reference to FIG. 10A by means of push buttons 27A (for the first switch mechanism A) and 27B (for the second switch mechanism B). These push buttons 27A and 27B are in contact with the bottom surface of the slider 28 and are individually pushed downward if the slider 28 is moved to the left as shown in FIG. 12A according to the contour (or the position of the thick portions) of the slider 28. The slider 28 has an upward protrusion 29 that engages with the tip of the downward protrusion 7 of the knob 3 and slides in the left-right direction according to the movement of the knob 3 into the UP and DOWN conditions.
In other words, as the knob 13 of this switch device 1 is raised into the UP condition, the slider 28 slides to the left and the push button 27A in contact with its thick portion along line 11C—11C is pushed downward, thereby establishing an open condition between the moving contact 19 and the NC contact 23 of the first switch mechanism A while maintaining a closed condition between the moving contact 19 and the NO contact 21.
If the finger is released from the knob 3 to set it in its neutral condition, the slider 28 slides to the right to return to its original position, causing the push button 27A to move upward and the moving contact 19 and the NC contact 23 of the first switch mechanism A to be in the closed condition.
If the knob 3 is pushed down to set it in the DOWN condition, the slider 28 slides to the right and the push button 27B in contact with its thick portion along line 11D—11D is pushed downward, thereby establishing an open condition between the moving contact 20 and the NC contact 24 of the second switch mechanism B while maintaining a closed condition between the moving contact 20 and the NO contact 22. If the finger is released from the knob 3 thereafter to set it in its neutral condition, the slider 28 slides to the left to its original position, causing the push button 27B to move upward and the moving contact 20 and the NC contact 24 of the second switch mechanism B to be in the closed condition.
When the knob 3 is in the neutral condition, the contacts of the first and second switch mechanisms A and B are in conditions as shown in FIG. 10B, that is, the moving contact 19 and the NC contact 23 of the first switch mechanism A are in the closed condition and the moving contact 20 and the NC contact 24 of the second switch mechanism B are in the closed condition. Under this condition, the DC motor 2 is not connected to the +B line 17 and hence the DC motor 2 does not rotate.
When the knob 3 is in the UP condition, the contacts of the first and second switch mechanisms A and B are in conditions as shown in FIG. 12B, that is, the moving contact 19 and the NO contact 21 of the first mechanism A are in the closed condition and the moving contact 20 and the NC contact 24 of the second switch mechanism B are in the closed condition. Under this condition, a closed circuit is formed from the +B line 17 to the DC motor 2 to the grounding line 18, and the DC motor 2 rotates in the direction of closing the window.
If the knob 3 is in the DOWN condition, although not shown, the moving contact 19 and the NC contact 23 of the first switch mechanism A are closed and the moving contact 20 and the NO contact 22 of the second switch mechanism B are closed. Under this condition, a closed circuit is formed from the grounding line 18 to the DC motor 2 to the +B line 17, and the DC motor 2 rotates in the direction of opening the window.
Although an example has been explained wherein the rotation of a DC motor is controlled by a single switch unit, there are also switch devices, depending on the kind of automobiles, allowing the window on the rider's side or the back windows to be controlled from the driver's seat. FIG. 13 shows a circuit structure for such a switch device, structured as a combination of a switch unit 9 for the driver and another switch unit 9′ for the rider such that the DC motor 2 for the window on the rider's side can be rotated or stopped not only by the rider but also by the driver.
Although an example was described above wherein a single terminal is assigned to each of the moving contacts 19 and 20 and the NC contacts 23 and 24 (that is, the common terminals 11 and 12 and the normally closed terminals 14 and 15) and a single normally open terminal 13 is assigned to both NO contacts 21 and 22 such that there are altogether five terminals, there are examples of other types such as shown in FIG. 14. The example shown in FIG. 14 is characterized wherein contacts connected to the grounding line 18 (the NC contacts 23 and 24 of the first and second switch mechanisms A and B) are connected together inside the unit and then pulled out from a single terminal 15a to be connected to the grounding line 18 such that there are altogether four terminals. Alternatively, two switch mechanisms each with one circuit may be used. In such a case, there are six terminals altogether.
Examples of prior art switch system described above with reference to FIGS. 10–14 may all be used without any trouble as long as they are used with a conventional 14V electrical system. If such a prior art switch system is used with a 42V electrical system, however, an overly strong current will flow between a specified pair of contacts at the return time from the UP condition to the neutral condition or from the DOWN condition to the neutral condition, thereby damaging these contacts.
FIG. 15 shows how such a damage may come about, FIG. 15A showing the switch device in the UP condition, FIG. 15B showing it at a moment immediately before its return to the neutral condition, and FIG. 15C showing when the switch device has returned to the neutral condition. They are different from the diagrams explaining the prior art operations in that a higher voltage (the source voltage of a 42V electrical system being 36V) is being applied to the +B line 17.
When the mechanism is in the UP condition as shown in FIG. 15A, the NO contact 21 and the moving contact 19 of the first switch mechanism A are in the closed condition and the moving contact 20 and the NC contact 24 of the second switch mechanism B are similarly in the closed condition. As a result, a closed circuit is formed from the +B line 17 to the DC motor 2 to the grounding line 18 and the DC motor 2 rotates in the direction of closing the window. When the driver's finger is released from the knob 3, the NO contact 21 and the moving contact 19 of the first switch mechanism A are released from their closed condition and the moving contact 19 begins to move towards the NC contact 23 while generating small arc discharges between the NO contact 21 within an allowable range until finally the moving contact 19 and the NC contact 23 of the first switch mechanism A come to be in the closed condition as shown in FIG. 15C. The source voltage then ceases to be supplied to the DC motor 2 and the rotation of the DC motor 2 stops.
In the case of a prior art switch device, the contact gap is as small as about 0.5 mm and hence cannot support an arc discharge voltage of about 42V. Thus, the moving contact 19 is in the condition of having a voltage of several volts applied thereto when it becomes connected to the NC contact 23. By experiments carried out by the present inventors, it was discovered that a large current of over 100A will flow from the moving contact 19 to the grounding line 18 through the NC contact 23 over a very short period of time such as about 0.5 ms (as indicated by a thick arrow 31 in FIG. 15C and that this results in a large discharge (indicated by numeral 32) between the NO contact 21 and the NC contact 23, thereby damaging or destroying the moving contact 19 and the NC contact 23.
Since this phenomenon will impede the popular acceptance of 42V electrical systems, its elimination has been a technical problem to be solved as quickly as possible.
In general, the gap between contacts is made wider as the applied voltage is increased in order to prevent arc discharges. If the gap is increased to about 4 mm, the arc discharge voltage may be accordingly increased and the moving contact 19 can be connected to the NC contact 23 while no voltage is applied thereon. If the gap is thus increased, however, the switch unit as a whole becomes large and may be inconvenient for being used on a vehicle.